When reference is made to multicomponent filaments here, I mean filaments that are composed of a plurality of different thermoplastic synthetic resin components and especially components with different properties like thermal coefficient of expansion, heat-induced shrinkage and the like. These components can be of the same synthetic resin, for example, polyesters of different compositions or polyethylenes or polypropylenes of different properties, or components of different synthetic resins, like, for example, a polypropylene component and a polyethylene component. A reference to a bicomponent filament is intended to mean a filament that has only two different thermoplastic synthetic resins.
A cross section through such filaments will show the two components, usually in a side-by-side relationship and the separation between the two synthetic resins generally will extend over the entire length of the filament.
Spun bond here is intended to mean webs that are formed from continuous filaments as well as webs that may be formed from less than continuous filaments, i.e. filaments that may have various lengths and need not be continuous.
In the usual production of spun bond, i.e. webs formed from mats of such continuous or semicontinuous filaments, the mats or fleeces have the filaments thereof bonded together at cross-over points. One of the properties that is generally of importance in such webs is the bulk of the filaments. The bulkiness property in some cases leaves much to be desired.
In general, the filaments are extruded from a spinneret, are stretched, generally by entrainment with air, and are collected on a foraminous surface on which the mat is formed and on which the filaments are bonded at their crossing points.
In conventional spun-bond processes, the bulkiness may not be sufficient, the mechanical properties of the web may not be satisfactory and neither may be fully reproducible. As a consequence, in earlier processes, there may be an excessive reject rate.